/**
 * It sets the p[i] equal to the sum of c[0] through c[i-1].
 *
 * @param {Array}   ptr             The Sparse Matrix ptr array
 * @param {Array}   c               The Sparse Matrix ptr array
 * @param {Number}  n               The number of columns
 *
 * Reference: http://faculty.cse.tamu.edu/davis/publications.html
 */
export function csCumsum(ptr, c, n) {
  // variables
  var i;
  var nz = 0;

  for (i = 0; i < n; i++) {
    // initialize ptr @ i
    ptr[i] = nz; // increment number of nonzeros

    nz += c[i]; // also copy p[0..n-1] back into c[0..n-1]

    c[i] = ptr[i];
  } // finalize ptr


  ptr[n] = nz; // return sum (c [0..n-1])

  return nz;
}